Rotatographic radiation apparatus having compensating grid plate



. Dec. 23, 1969 TADAYOSHI MATUDA ETAL 3,486,022

ROTATQGRAPHIC RADIATION APPARATUS HAVING CQMPENSAIING GRID PLATE Filed July 17, 1967 FIG. I

nun-w lux/p4 J'Msso E 9 1 any/0 WWW/V4 Ifrmvf/V454/ INVENTORS 3,486,022 ROTATOGRAPHIC RADIATION APPARATUS HAVING COMPENSATING GRID PLATE Tadayoshi Matuda and Shigeo Endo, Toyohashi-shi, Sumio Makino, Yokohama-shi, and Katsumi Nagai, Tokyo, Japan, assignors to Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan, a corporation of Japan Filed July 17, 1967, Ser. No. 653,922 Claims priority, application Japan, July 23, 1966, 44/ 48,233 Int. Cl. Htllj 37/22; G01n 23/04, 23/00 US. Cl. 25053 2 Claims ABSTRACT OF THE DISCLOSURE In a radiation rotatographic apparatus wherein a crosssection perpendicular to the axis of a body to be examined is photographed by projecting X-rays at an angle with respect to the cross-section, a scattering eliminating grid plate is disposed across the path of X-rays between the cross-section and a photographic film holding mechanism, the thickness of said grid plate being increasingly varied corresponding to the distance between the radiation receiving surface of the film and the source of X-rays whereby to produce an image of uniform concentration.

This invention relates to a rotatographic apparatus in which an image of a cross-section perpendicular to the axis of a human body is photographed by projecting X-rays to the cross-section at an angle with respect thereto.

Present problems involved in such a rotatographic apparatus is the non-uniform concentration of the photographed image throughout the cross-section when the photographic film is developed. Usually when a tomograph of the waist of the body is taken while lying on its back the concentration is higher in the abdominal region than in the back region. This is contradictory to the desire of the medical examiner that images of both of the diseased part and of the peripheral portions of the body should appear on the film at proper concentrations. More particularly, should the period and/ or quantity of irradiation of X-rays be controlled to obtain an image of the back region of appropriate concentration the concentration of the image of the abdominal region photographed on a film would reach to the saturation value of the fi m, thus making it impossible to clearly determine the configuration of the abdominal region.

Among factors that cause such a difficulty may be mentioned the integrated value on the photographic film of the degree of attenuation of X-rays that are transmitted through various portions of the human body as well as the distance between a source of X-rays and the surface of the photographic film. As the square of the distance between the source of X-rays and the surface of the film is inversely proportional to the brightness of the X-rays on the surface of the film, this is an important factor to be obviated.

This invention contemplates to provide an X-ray rotatographic apparatus wherein the radiation receiving surface of a photographic film spaced from a source of X-rays is disposed in parallel with a cross-section to be examined which is perpendicular to the axis of a human body, and wherein a scattering eliminating grid plate is disposed across the path of X-rays, the thickness of the grid plate being tapered such that it is thin at regions of X-rays path corresponding to portions of the film which are remote from the source of X-rays thus minimizing the attenuation of X-rays whereas thick at regions of X-ray path corresponding to other portions on the film which are closer to the source of X-rays thus increasing the attenuation of X-rays.

nited States Patent section to be examined at appropriate concentrations, thus enabling accurate determination of the positions of the diseased part with reference to the peripheral portion of the patients body.

Tapered plates of lead or an alloy essentially consisting of lead are preferable for said scattering eliminating plate.

Further objects and advantages of the present invention will become apparent and the invention will be better understood from the following description, reference being made to the accompanying drawings, in which:

FIG. 1 is a diagram to represent relative positions of a source of X-rays which cross a cross-section perpendicular to the axis of a patients body to be examined by an X-ray rotatographic apparatus and the surface of a photographic film receiving said X-rays;

FIG. 2 is a diagrammatic side view of a radiation rotatographic apparatus constructed in accordance with the principle of this invention; and

FIG. 3 is a perspective view of one example of the scattering eliminating plate employed in the apparatus shown in FIG. 2.

Referring now to the accompanying drawing FIG. 1 shows the relative position among a cross-section A of a body 1 to be photographed, a source of X-rays 2 and the radiation receiving surface of a photographic film 3. A conventional X-ray tube may be used as the source of X-rays and radiations therefrom reach the radiation receiving surface of the film. Images of the portions a and b included in the cross-section A are projected upon the radiation receiving surface at points a and b respectively.

Distances between the X-ray tube and respective points al and b are represented by -F-a and i -b respectively, where F representing the radiation point of the X-ray tube and F-a Fb Neglecting the attenuation of X-rays caused by the body being examined brightness of X-rays at the point a would be higher than that at the point a would be higher than that at the point b thus resulting in an extremely dark image at point a and very pale image at point b on the developed film, the concentration of the image gradually decreasing from point a to point b As a consequence, Where it is desired to obtain a clear image at point 12 the concentration at the point a, would reach the saturation value, thus obscuring the whole image of the cross-section.

Turning now to FIG. 2, the, X-ray rotatographic apparatus comprises a bed plate 10 which is supported by a pedestal 11 slidable in the directions indicated by an arrow. An object to be examined, a human body 12, for example, is supported on the bed plate 11. Above the bed plate is located an X-ray tube 13 supported by an arm 16 which, in turn, is mounted on a horizontal shaft 15 journalled on a base 17. The lower end of the arm 16 carries a film holding mechanism 14. An upwardly extending arm 19 is connected to one side of the holding mechanism 14 to support a scattering eliminating or preventing grid plate 18 of lead or a metal plate essentially consisting of lead, said grid plate being positioned across the passage of X-rays emanating from the X-ray tube 13. As clearly indicated by FIG. 3 the grid plate 18 in the form of a tapered plate, the ratio of bottom side il to top side h being related to the length of paths of X-rays F-a and Fb corresponding to points a and b on the film surface. The grid plate 18 functions to attenuate X-rays in accordance with its thickness.

Thus, by positioning the grid plate 18 such that its bottom and top correspond to points a and b respectively,

on the film surface, X-rays passing through the portion adjacent to bottom would be attenuated greatly whereas those passing through the portion near top slightly, thus assuring uniform concentrationof the developed image from point a to point 17 notwithstanding the difference in the distance of travel of X-rays at respective points, thus substantially eliminating above mentioned defects in X-ray photographs caused by the difierence in the distance from the source of X-rays to various points on the photographic film.

It should be understood that above described embodiment is illustrated to explain the principle of this invention and that many alterations and modifications may be made without departing from the true spirit and scope of this invention.

What is claimed is: 1. A radiation rotatographic apparatus comprising: a bed for supporting an object to be examined; an X-ray source for irradiating X-rays on said object, said X-ray source being rotatable around said object;

an X-ray film disposed on the opposite side of said object with respect to said X-ray source for receiving X-rays passed through said object;

a rotatable supporting arm for supporting said X-ray film and said X-ray source to locate said X-ray film and said X-ray source on opposite sides of said object; and v a tapered scattering eliminating grid plate for equalizing the strength of the X-rays irradiated onto said X-ray film, said grid plate being mounted on said supporting arm and interposed between said object and said X-ray film. 2. The radiation rotatographic apparatus according to claim 1 wherein said scattering eliminating plate is made of a thin plate essentially consisting of lead.

References Cited UNITED STATES PATENTS 2,405,444 8/ 1946- Moreau et a1. 25086 2,407,938 9/ 1946 Schonander 25062 3,248,547 4/1966 Van de Geijn 25086 00 RALPH G. NILSON, Primary Examiner A. L. BIRCH, Assistant Examiner U.S. ,Cl. X.R. 

